1. Technical Field of the Invention
The present invention relates to a control apparatus for controlling a fuel injection apparatus; the latter includes an accumulator for accumulating high-pressure fuel, at least one injector for injecting the high-pressure fuel accumulated in the accumulator into a cylinder of an internal combustion engine, and a pressure sensor for sensing the fuel pressure in the accumulator.
2. Description of the Related Art
There is known a fuel injection apparatus that includes a common rail (i.e., a common accumulator) for accumulating high-pressure fuel, a plurality of injectors for injecting the high-pressure fuel accumulated in the common rail into corresponding cylinders of a diesel engine, and a pressure sensor for sensing the fuel pressure in the common rail.
In such a fuel injection apparatus, it is possible to suitably set a target value of the fuel pressure in the common rail according to the operating condition of the engine; thus, it is also possible to suitably control the pressure of fuel supplied to injectors.
Moreover, there is also known a control apparatus that controls the fuel injection apparatus by manipulating the injectors.
Specifically, the control apparatus is configured to set, for each of the injectors, a command injection duration (i.e., a command value of fuel injection duration) on the basis of a command injection quantity (i.e., a command value of fuel injection quantity) and a value of the fuel pressure in the common rail sensed by the pressure sensor. More specifically, the fuel injection quantity of the injector depends not only on the injection duration but also on the fuel pressure in the common rail; in other words, there is a certain relationship among the injection quantity, the injection duration, and the fuel pressure. Therefore, it is possible for the control apparatus to determine the command injection duration on the basis of the relationship among the three parameters. After that, the control apparatus manipulates the injector to open for the set command injection duration, thereby injecting the command injection quantity of high-pressure fuel into the corresponding cylinder.
Furthermore, the fuel pressure in the common rail generally varies with time. To suitably control the fuel injection apparatus regardless of the variation in the fuel pressure, there is disclosed a method in Japanese Patent First Publication No. 2001-152949. According to the method, the control apparatus is further configured to: 1) set a preliminary command injection duration on the basis of a first value of the fuel pressure which is sensed by the pressure sensor before an energization of the injector; 2) set a final command injection duration on the basis of a second value of the fuel pressure which is sensed by the pressure sensor when the energization of the injector starts. With this configuration, it is possible for the control apparatus to more suitably set the command injection duration (i.e., the final one) on the basis of a value of the fuel pressure (i.e., the second value) which is sensed at a timing as close to the actual fuel injection as possible.
However, when feed durations, during which a fuel pump feeds the high-pressure fuel into the common rail, overlap with the injection durations of the injectors, the fuel pressure in the common rail will be changed not only due to the fuel injections by the injectors but also the fuel feeds by the pump. Therefore, in such a case, it may be difficult to suitably set the final command injection duration on the basis of the second value of the fuel pressure which is sensed at the start of the energization. In particular, in an asynchronous fuel injection system where the feed durations are not in one-to-one relationship with the injection durations, there will be part of the injectors whose injection durations overlap with the feed durations and the others whose injection durations do not. Accordingly, there will be part of the injectors which actually inject more fuel than the command injection quantity and the others which actually inject less fuel than the command injection quantity.